The invention relates to an extraction method for a casting mold or press mold, in particular an injection stamping mold for plastic, in which a plurality of mold parts having a negative mold of the molded part to be manufactured are moved by at least two drives, which can be activated in dependence on one another.
Such methods with a plurality of drives are required where complicated molded parts are to be manufactured, and these are known from practice. In the known method, hydraulic cylinders employed for moving the mold parts are mechanically coupled to one another. In consequence, the motions of the mold parts have a specified relationship to one another so that, for example, one of the molded parts is rotated by a certain angle while the other is displaced linearly by a specified distance.
A disadvantageous feature of the known method is that it is very expensive to carry out because the mechanical coupling of the motions of the drives demands a very high level of structural complexity. Despite this complexity, damage to the molded part can occur due to parts of the molded part breaking. Incomparably more dangerous, however, is the case in which the molded part has an incipient fracture. Such damage cannot be recognized immediately and leads to the molded part only fracturing at a later date as a constituent part of a subassembly during the operation of the subassembly, so that the complete subassembly fails.
Renewed structural expenditure is necessary in each case in order to couple the motions of the drives for the manufacture of different molded parts. In addition, with the known method it is only possible to make an inaccurate allowance for shrinkage of the molded part. This often leads to damage to the molded part when it is extracted from the mold.
The invention is based on the problem of designing a method, of the type quoted at the beginning, in such a way that it can be matched to almost any given molded parts in the simplest possible manner and reliably avoids damage to the molded part during extraction from the mold.
In accordance with the invention, this problem is solved by a control device, for moving the mold parts, determining the position of the mold parts and comparing it with electronically stored motion curves and/or motion sequences and activating the drives as a function of the comparison.
By means of this design, the motions of the mold parts are determined by the control device in accordance with the motion curves. Mechanical coupling of the drives is therefore not necessary. Apart from the new calculation, therefore, no further expenditure is necessary when a new molded part has to be manufactured. The shrinkage of the molded part when it cools in the mold can, for example, be determined using experience values. The values from the motion curves can subsequently be compared with the experience values. The danger of damage to the molded part during its extraction from the mold is kept particularly small by means of the invention. In consequence, it is very simple to carry out the method according to the invention. The structural requirements for carrying out the method are particularly small due to the employment of the control device. By means of the invention, vane wheels of peripheral-duct pumps provided with a large number of undercuts and generated by the injection stamping process can be extracted from the mold without damaging the guide vanes.
The method according to the invention can be used at particularly low cost where the motion curves and/or the motion sequences are taken from an electronic memory.
The method according to the invention can be applied to almost any given design of molded parts if the motion curves and/or the motion sequences are calculated by a simulation computer to correspond with the molded part to be manufactured. By this means, a mold provided for carrying out the method according to the invention can be easily reprogrammed after the mold parts have been exchanged.
In accordance with an advantageous development of the invention, the molded parts can be moved with particular accuracy if the control device controls electric motors connected to the mold parts. By this means, the inaccuracy in the movement of the mold parts caused by leakage, for example, due to a hydraulic installation, is avoided.
Another advantageous development of the invention contributes to the further increase in the accuracy of the motion of the mold parts, using the track curves provided, if the control device supplies a series of step pulses to the electric motors for the stepwise motion of the mold parts.
The structural complexity for the control device and the memory can be kept particularly small, in accordance with another advantageous development of the invention, if the motion of the mold parts is measured in steps and if the control device converts the motion curves into target points for the electric motors. The motions of the mold parts and the sequence in time of the motions can be very simply fixed in this way.
The danger of destruction of the molded part to be manufactured can be kept particularly small if, in accordance with another advantageous development of the invention, the control device records an unintended contact between the mold parts and the molded part and at least switches off the drive causing the contact. The recording of the unintended contact with the molded part can, for example, take place by means of regular monitoring of the electric current taken by the electric motors. As an alternative to this, sensors, which determine the power expended for the motion of the mold parts, can be arranged in the drives.
The invention permits numerous embodiments. One of them is represented in the drawing and is described below for further clarification of the basic principle.